Lab Final Flashcards
Green chemistry
an approach to chemistry that aims to maximize efficiency and minimize hazardous effects on the environment and human health
Where do Emory shuttles get fuel for shuttles?
160 tons of fryer oil and grease were collected in 2017 and made into biofuel for Emory’s shuttles
*uses B5
Why is B80 used in the cold instead of B100?
Diesel is more viscous so it makes more sense to use a lesser proportion of biodiesel when it is cold
Chemical composition of fatty acids
RC(=O)OH
R: long chain hydrocarbon
Why can you not just use animal fats as fuel?
They are solids or viscous at room temperature (saturated fats)
Need to make able to flow
Unsaturated fatty acids
long chains that contain a C=C double bond
Is anything a pure saturated fat?
Rarely and the kinks make it difficult to pack triglycerides
What is the red diamond in old hazard label?
Flammability
What is the blue diamond in old hazard label?
Health
What is the white diamond in old hazard label?
Special notice
ex: reacts with water in unstable manner
What is the yellow diamond in old hazard?
Instability/reactivity
Comparison of butanol vs. ethanol as fuel
Butanol has more carbon chains so more energy produced
Ethanol produces more CO2
What was our biodiesel?
a methyl-ester
Difference between temperature and heat?
Temperature is a measure of molecular motion or kinetic energy
Heat is a transfer of thermal energy between two objects due to differences in temperatures
Intermolecular forces in methanol
hydrogen bonding (oxygen)
dipole-dipole
dispersion
Intermolecular forces in canola oil
mostly dispersion
some dipole-dipole due to ester groups
Heat of combustion units
kJ/g
How to find heat of combustion?
Normally take how many kJ to heat water and divide by grams of biodiesel, etc.
Why is biodiesel said to be carbon-neutral although it produces CO2?
Since biodiesel is made from rapeseed and not fossil fuels, it is said that the carbon the rapeseed absorbs during its lifetime is equal to the CO2 released
no net addition to the atmosphere
Why is the methanol and the canola oil able to mix?
the canola oil contains an ester bond that makes it slightly polarized
Why is biodiesel less viscous than starting triglyceride?
it is a smaller molecule
Kinetics
applies to the SPEED of a reaction
Thermodynamics
applies to the EXTENT of a reaction, the concentration of product that has appeared after an unlimited time
Fetal hemoglobin
More efficient at binding O2
Has a larger K value
Beer-lambert equation
A = elc
Molar absorbitivity constant
e in Beer’s Lambert equation
3 ways to stress a system
- Temperature
- Concentration
- Pressure
How do you measure concentration through absorbance when equilibrium is dynamic (i.e. there will never be purely products)?
Put in so much of one of the reactants so that the system is essentially driven to completion
How do you determine the wavelength to set spectrometer to for an unknown compound?
Look at the peaks of absorbance on scanning setting
What should you use as your blank to measure concentration of FeSCN2+ ?
Highest concentration of iron
What should you do to calculate concentration when not given much information?
M1V1=M2V2
What happens to the amount of acid when base is added?
Amount of acid decreases
How to calculate enthalpy when K was calculated at 2 different temperatures?
Van Hoff’s Equation
What is the gas constant, R?
.008314 kJ/mol
or
8.314 J/mol
What happens when you add silver nitrate to an anion?
Often makes a white precipitate
Ag(anion)
What is borax?
a slightly soluble salt
How to determine K when there are two products?
Formula looks like: K = [A]2[B]
Can use the mol ratio to substitute
Know that for every 1 mol B, there are 2 mols A
K = [A]2[2A]
How can we calculate K by titration?
use the known concentration of the acid/base to solve for the concentration we are looking for
End point
is when the color changes, indicating the end of the titrant
Equivalence point
when the number of moles of acid is equal to the number of moles of base
Titration using a mass burette vs. titration using a volumetric burette
same calculations except one using volume and the other uses mass
Why do we use different indicators?
Different indicators are sensitive to different pHs
Phenol red is sensitive to ~7
Phenophtalein is sensitive to ~9
How do you determine the temperature of a solution if you have to measure its absorbance?
measure the temperature before and after sampling in the spectrometer
Why does it not matter how much water is used to move a sample to a flask for titration?
the number of moles of the substance studied will remain the same
Why do we not use M1V2=M1V2 with the acid and base for a titration?
This assumes that there is a 1:1 mol ratio between the acid and base which we do not know
Amount of titrant needed when solubility increases?
Less soluble = less titrant
More soluble = more titrant
What are the units of entropy?
J/K
What happens if extra borax was transferred to the flask for titration?
more borate = larger K
larger K = less free energy, since G=-RTln(K)
Where is the buffer region of a titration curve?
the flat line leading up to the spike to the equivalence point
at this point there is conjugate acid and conjugate base present
If you titrate a weak acid with a strong base, what is true of the equivalence point?
all of the weak acid would have been converted to conjugate base
What is true of halfway to the equivalence point?
there are equal amounts of conjugate acid and base
use Henderson-Hasselbach equation…you have a buffer!!
Why does Ka decrease as starting pH increases of a titration?
a higher starting pH indicates a weaker acid and therefore it is not as reactive
Rate of reaction
speed at which reactants are converted into products
M/s
kinetics
What is the central focus of chemical kinetics?
reaction rates
If given a graph of concentration vs. time, how do you find the reaction rate?
take the slope
rate = d(concentration)/dt
What would result in the rate change being a decrease by a factor of 4?
A reaction is second order with respect to reactant B and B is halved
5 factors that affect rate
- Nature of reactants
- Temperature
- Catalyst
- Concentration of reactants
- surface area of reactants
Effect of surface area on concentration
Greater the surface area, the faster rate of reaction
More particles are exposed to attack by other reactant particles
Arrhenius plot
ln(k) vs. 1/T
- use slope to calculate activation energy
- use y-intercept to calculate A
How do catalysts work?
New mechanism
Lowers activation energy (resulting increases k)
They increase the rate of both the forward and the reverse reactions
Relationship between activation energy and k
inverse relationship
Relationship between temperature and k
direct relationship
Surface catalyst
a solid that speeds up a reaction between gases
What is slope in a first order reaction plot of ln(A) versus time?
slope = -k
What is slope in a second order reaction plot of 1/A versus time?
slope = k
What is slope in a zero order reaction plot of A versus time?
slope = -k
How to determine the reaction order by graphing?
Graph A vs. t, ln(A) vs. t, and 1/A vs. t
- each correspond to a different order respectively
- known as integrated rate laws
What is the limitation of the integrated rate laws?
Can only work for a single variable
How to rearrange pseudo-rate laws?
flood the system with A, so there is basically no change in A
rate = ko [B]^n
What does K observed equal?
ko = K[A]^m
*A is what the system was flooded with
Beer’s Law Plot
Absorbance vs. Concentration
How to determine the molar absorbvitity constant?
use the slope of the Beer’s plot
Redox process in ionic compounds
there is a complete change in electrons
Redox process in covalent compounds
there is a shift in electrons
Oxidizing agent
is reduced
gains electrons
Reducing agent
is oxidized
looses electrons
Oxidation number
a number assigned to a chemical that represents the number of electrons gained or lost (if the number is -)
Electromotive force
E cell
the cell voltage or cell potential
*can occur due to flow of electrons between the anode and cathode
Anode
where oxidation occurs (loosing electrons)
is denoted on the left in a standard diagram
Cathode
where reduction occurs (gaining electrons)
is denoted on the right in a standard diagram
Galvanic or voltaic cells
produce electricity as a result of spontaneous reactions
Electrolytic cells
non-spontaneous chemical change driven by electricity
An Ox and a Red Cat
An Ox: anode = oxidation
Red Cat: cathode = reduction
Cats are +
Cathode is positive
Why does a voltaic cell work?
the spontaneous reaction occurs as a result of different abilities of materials to give up their electrons
Cell voltages
the potential differences between the electrodes
The Standard Hydrogen Electrode
an arbitrary 0 chosen to compare potentials of individual electrodes
Colors of Manganese in Different Oxidation States
\+7 = magneta \+6=green (Arnold) \+5=yellow (or blue) (Tina) \+4=clear w/ brown precipitate \+3=pink \+2=clear w/ no precipitate
What is the relationship between oxidation number and reducing ability?
greater oxidation number = greater reducing agent
a higher oxidation number means that it lost the most electrons, which means that it donated the most to another substance. it did the most reducing
When can you compare oxidation number and reducing ability of different substances?
they have to be reducing the same substance
What happens if two samples are contaminated in the murder mystery experiment?
the stronger reducing agent (higher oxidation number) will mask the color of the weaker reducing agent
the stronger reducing agent is more reactive
Ferromagnetic electron spin
unpaired electron spins from the atoms in the solid (represented by arrows) align with each other within regions called magnetic domains
Ferrimagnetic electron spin
within each magnetic there are two spins in different directions
However, they do not cancel out and this leaves a net magnetism
Did we use a ferromagnetic or ferrimagnetic substance?
Magnetite is a ferrimagnetic substance
Superparamagnetic
the magnetic domains are the particles themselves
all the electrons within a given particular spin in the same direction
*ferrofluids are superparamagnetic and this makes them magnetize and demagnetize more rapidly
Why do ferrofluids form peaks?
they are part of a colloidal suspension that always has small waves constantly present on the surface of a ferrofluid
these waves are amplified in the presence of a magnetic field
Reaction mechanisms definition
a step-by-step description of actual events (often collisions) in an overall chemical reaction
What does every step of a reaction mechanism do?
Alters a molecules geometry, energy, or produces a new molecule
Why do trimolecular processes rarely occur?
the probability of 3 molecules colliding at the same time is incredibly rare
Order in a rate law for an elementary process
are the same as the stoichiometric coefficients for an elementary process
Intermediates
produced in one step and consumed in another
Rate determining step
one elementary step is usually slower than all others
SN1 mechanism
2 step mechanism
produces an intermediate
1st order reaction
SN2 mechanism
1 step mechanism
does not have an intermediate
2nd order reaction
Chemical formula of magnetite
Fe3O4
Suspension
a heterogenous mixture that has solid particles large enough to settle to the bottom
Colloid
a solution that has evenly distributed particles large enough to remain suspended, but do not settle to the bottom
Surfactant
a compound that is added to a liquid to lower its surface tension
ex: detergents
Hydracids
an acid that does not contain an oxygen
composed of hydrogen and a nonmetallic element
ex: HF
Solvolysis Reaction
a substitution reaction where the solvent is a nucleophile
Why is a surfactant used in making your ferrofluid?
a surfactant prevents the particles of magnetite from clumping together (agglomerating)
can’t have agglomeration because they need to be equally suspended throughout the solution
Why are Fe(ii) and Fe(iii) not magnetic?
their electrons move independently of one another and do not contain large regions where the electron spins are alligned
In the SN1 reaction experiment, what were the controls? What did they control for?
- Not heated test tube. Controlled for tert-butyl’s natural reaction with ethanol without heating.
- No alykl halide added. Controlled for the heating effects of ethanol and the indicator
3 alkyl halides reactivity with ethanol
3º, 2º, 1º
*decreasing order. 3º is the most reactive
Why did only tert-butyl react with the AgNO3?
tert-butyl has an SN1 mechanism, so when the carbocation intermediate is formed, there is a free halide to combine with the silver and form a precipitate
3 steps of SN1 reaction
- Formation of carbocation
- Nucleophilic addition of alcohol
- Deprotonate by solvent
Why is tert-butyl the most reactive with ethanol
It has a carbocation intermediate that is highly unstable
What happens within the atom when it is fluorescing?
Atom gets excited to a higher energy level and then it emits light when it falls from these higher energy levels
Who was awarded the nobel prize in chemistry 2008?
Martin Chalfie, Osamu Shimomura, Roger Y. Tsien
How are GFPs used in biology?
can be attached to proteins to see if gene splicing/gene expression worked
What did Roger Tsien do?
changed the structure of GFP to produce proteins that glowed cyan, blue, and yellow
What did Martin Chalfie do?
used GFP to label neurons in C. elegans
Who was the first genetically modified primate?
ANDi
statistically very hard to accomplish
What is the structure of GFP?
green flourescent protein consists of 238 amino acids folded in the shape of a beer can
the ends of the chain interact in the middle to create the light (chromophore)
Fluorescence
lumination that is due to quickly absorbing high energy light and releasing two or more photons
Phosphoresence
lumination that occurs more slowly over time
Coordination number
the number of ligand atoms that are bonded directly to the central metal ion
Geometry
the geometry (shape) of a complex ion depends on the coordination number and nature of the metal ion
Ligand atoms
an ion or molecule that binds to a central ion in order to form a coordination complex
Donor atoms per ligand
molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.
What properties do ligands have?
they are lewis bases
they are able to donate a pair of electrons
Monodentate ligands
use one pair of electrons to form one point of attachment to the metal ion
Bidentate ligands
use two pairs of electrons to form two points of attachment with the metal ion
*can go up to tetradentate, etc.
Asymmetric synthesis and when it is utlized
using chiral reagents, catalysts, and fragments to produce SINGLE enantiomeric configuration
this approach is used when dealing with big biomolecules
Chromatographic resolution of enantiomers
requires an optically active (chiral) stationary phase that allows passage of one enantiomer while the other is held up on the column.
applicable when dealing with a small amount of material
Resolution by crystallization
*what we did
diastereomer formation followed by product enrichment by the selective crystallization of one diastereomer over the other.
What is the blank for the polarimeter?
Water
What does Co(en)3 represent?
C6 H24 N6 Co
What is the purpose of a solvent/moisture trap in a vacuum filtration?
Capture solvent that could have been sucked into the line, so the solvent does not destroy the pump
What is the purpose of hydrogen peroxide in the preparation of Co(en)3 3+?
hydrogen peroxide works as a oxidizing agent
oxidizing Co(ii) to Co(iii)
two major safety hazards of the first experiment?
not to come into contact with sodium hydroxide and hydrogen peroxide
After the (+) enantiomer was isolated, why did you have to precipitate the iodide salt out of it?
If we dissolved the crystals into the solution, we would have had additional molecules that can rotate light, so we had to isolate the Cobalt from the tartrate
